1. Field of the Invention
The present invention relates to field emission cathodes and methods for fabricating the same and, particularly, to a carbon nanotube film based field emission cathode and a method for fabricating the same.
2. Discussion of Related Art
Carbon nanotubes (CNT) are a novel carbonaceous material and received a great deal of interest since the early 1990s. Typically, carbon nanotubes have tube-shaped structures with small diameters (less than 100 nanometers) and large aspect ratios (length/diameter). The carbon nanotubes have excellent electrical properties as well as excellent mechanical properties. The electronic conductance of the carbon nanotubes is related to their structures. Carbon nanotubes can transmit extremely high current density and emit electrons easily, at low voltages, less than 100 volts. Thus they are considered to be promising for use in a variety of display devices, such as field emission display (FED) devices.
Generally, a CNT field emission display device includes a cathode electrode and a carbon nanotube array formed on the cathode electrode. The methods adopted for forming the carbon nanotube array on the cathode electrode mainly include in-situ synthesis methods and printing methods.
An in-situ synthesis method is performed by coating metal catalysts on a conductive cathode electrode and directly growing carbon nanotubes on the conductive cathode electrode by means of chemical vapor deposition (CVD). However, the carbon nanotubes synthesized on the cathode electrode inevitably entangle with each other. Thus, the field emission characteristics of the carbon nanotube array are generally unsatisfactory.
A printing method is performed by printing a pattern on a conductive cathode electrode using carbon nanotube based conductive paste or organic binder. The carbon nanotubes can extrude from the pattern to form emitters by a series of treating processes. However, the density of the effective carbon nanotube emitters is relatively low, and the carbon nanotubes entangle with each other and are oblique to the conductive cathode electrode. Furthermore, the treating processes may include a step of peeling the paste off to form extrusions of the carbon nanotubes. Such peeling step may damage the carbon nanotubes and/or decrease their performance. Thus, the efficiency of electron emission is relatively low, and controllability is often less than desired. Still furthermore, the printing method has relatively high cost.
What is needed, therefore, is to provide a field emission cathode and a method for fabricating the same, in which the field emission cathode has a stable field emission performance and a high efficiency, and the method can be utilized easily and at a low cost.